Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

008
FXUS63 KLOT 172328
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
628 PM CDT Wed Jun 17 2026

.KEY MESSAGES...

- Tranquil weather is expected to close out the work week in the
  wake of this system.

- Another strong storm system is expected to bring a return of
  showers and thunderstorms later this weekend, with some
  potential for heavy rainfall and/or severe weather somewhere
  in the general region.

&&

.DISCUSSION...
Issued at 211 PM CDT Wed Jun 17 2026

Early this afternoon, we find a widespread mess of showers and
a few embedded thunderstorms falling on the area east of a
double-barreled surface low centered over IA and MN. These
showers have been riding along the MUCAPE gradient as it
spread east across northern IL on the nose of the low level
warm conveyor. A surface warm front is extending across central
IL south of the CWA with higher thunder coverage near and south
of the front into the instability reservoir. The front continues
to sharpen up with time as strong theta-e advection hits it
from south. A lack of elevated instability extending north of
the front owing to poor lapse rates aloft accounts for the lack
of thunder coverage into northern IL. Nonetheless, strong
kinematic and low level upglide in a moisture-rich environment
allowed for widespread moderate to heavy rainfall across
northern IL through much of the morning. A wake low also
developed north of I-80 behind the departing heavier rain.
Strong southeast winds with gusts periodically over 50 mph
prompted us to issue a Wind Advisory for our northern CWA, but
they continue to gradually ease from west to east.

Still a somewhat tricky setup for this afternoon with
unresolvable mesoscale uncertainties looming through the next
several hours. The warm front, while sharpening with time, has
made little to no headway north or southward through about 1
PM. All eyes will be on the evolution of this boundary over the
next several hours as it will dictate the northern extent of the
much higher severe threat, including the appreciable tornado
and destructive wind threat, as additional storms are slated to
develop along and ahead of the approaching cold front. We`re
already seeing some pre-frontal development over SE IA which
could evolve into severe convection in the near term, especially
cells that stay along and south of the warm front. Latest CAM
guidance favors this front inching just northward into mid-
afternoon and opening up the far southern CWA to this higher
severe threat. However, enough of a signal remains to be
ignored, including a consistent one from the RAP, for the front
to surge farther north, possibly closer to I-80. At this time,
this does not look very likely, aside from perhaps a brief
window toward the late afternoon/early evening as the low center
works across and perhaps brings a brief window of ML instability
farther north later today.

The more impressive kinematic field will be found out ahead of
the front this afternoon. In fact, SPC mesoanalysis paints eye-
catching long, looping hodographs over northern and central IL
at the moment, we just don`t have the instability to make any
good use of that right now. Meanwhile, hodos straighten out
upstream toward the Mississippi thanks to a veering, weakening
low level wind field closer to the cold front. Any convection
that can initiate ahead of the front, such as along the pre-
frontal trough axis, will be exposed to a much more concerning
shear profile than activity along the front itself. Storms
currently developing over SE IA fit this mark and will need to
be watched closely as they progress across IL.

Put together, the threat for strong tornadoes and destructive
wind gusts is still alive and well, but now may be confined to
only the far southern portions of our CWA through the
afternoon. Namely, areas south of the Kankakee River are most
favored to reside along/south of the warm front and offer the
highest ceiling for severe weather over the next few to several
hours. Quickly stabilizing conditions should put a halt on the
tornado threat and highest wind threat north of the front, but
damaging winds will certainly be possible across northern IL
with elevated convection through the afternoon. The main window
for the severe potential in our CWA will be roughly 3 PM through
6 PM with additional, likely non-severe storms possible through
mid-evening along the cold front.

Additionally, the moisture-rich environment with PWATs just
under 2" across northern IL will lead to torrential rainfall in
thunderstorms and a threat for flash flooding. Strong dynamic
and kinetic forcing and efficient upglide along the elevated
face of the warm front will spread the heavy rain and flooding
threat north of the surface front. Guidance is consistent in
resolving over a widespread 1 inch+ of rain with areas of
higher totals very attainable. The highest QPF is favored near
and south of I-80. A Flood Watch is currently in effect outside
of our northern-most counties.

Gusty gradient winds will develop tonight behind the departing
low with wind 25 to 30 mph wind gusts forecasts for much of the
night. After this evening, rain-free conditions are forecast
into the weekend. Cooler-than-normal temperatures will begin
trending warmer over the coming days with lower 70s forecast
tomorrow with upper 70s/near 80 again by Saturday. Another
synoptic system is progged to move across the region in the
Sunday to Monday period. Previously, had been looking like
another decent opportunity for heavy rain and severe weather,
although latest medium range guidance has been trending south of
the area. Look for a more detailed analysis of this system in
future discussions once today is behind us.

Doom

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 628 PM CDT Wed Jun 17 2026

Aviation forecast concerns for the 00Z TAFs:

- TSRA potential has decreased markedly for the terminals. KRFD
  has perhaps a 20% chance of an isolated storm prior to 02Z.
  Even lower potential for TS at Chicago terminals prior to
  03-04Z.

- Period of MVFR ceilings ahead of a cold front this evening,
  and again early Thursday morning.

- Breezy south-southwest winds gusting 20-25 kts will become
  westerly behind a cold front this evening with gusts around 25
  kts persisting into Thursday morning before gradually
  diminishing.

Early evening surface analysis depicts low pressure over western
WI, with a cold front trailing south-southwestward approaching
the Mississippi River. While a few scattered showers/isolated
thunderstorm remain possible ahead of the front this evening,
the large rain-cooled footprint from earlier rain and storms
has greatly reduced low-level instability. Somewhat more
favorable instability/forcing exists over WI/northeast IA, and
the proximity of KRFD supports a slight (20%) TSRA potential
there. Farther to the southeast, TS chances for the Chicago
terminals are lower than that. Have maintained a PROB30 for SHRA
for all sites until cold frontal passage.

Moist low levels ahead of the front have allowed for rather
extensive MVFR ceiling development in the 1200-1600 ft range,
and this will likely continue until cold fropa. VFR conditions
are expected behind the cold front, though an area of MVFR cigs
is expected to spread into the terminals predawn then lift back
to VFR by mid-late Thursday morning.

Wind-wise, breezy south-southwest winds will turn west to west-
northwest behind this evening`s cold front, with gusts around 25
knots continuing through Thursday morning, before gradually
diminishing in the afternoon.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement until 4 AM CDT Thursday for ILZ006-
     ILZ103-ILZ104.

IN...Beach Hazards Statement from 1 AM CDT Thursday through
     Thursday afternoon for INZ002.

LM...Small Craft Advisory until 9 AM CDT Thursday for the IL and IN
     nearshore waters.

&&

$$

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